Sen. Richard Tisei, R-Wakefield, who represents Melrose Wards 1-5, had been working as the campaign chairman for Republican gubernatorial candidate and Swampscott resident Charles Baker since August.

Now, with Baker’s announcement Monday that Tisei will be his running mate in Baker’s 2010 Republican bid for the governor’s seat, Tisei is going from a coach on the sidelines to a player on the field.

At a news conference this morning at the Americal Civic Center in Wakefield, Baker was scheduled to announce Tisei as his running mate and candidate for lieutenant governor. The partnership was also announced Monday morning on Baker’s Web site, CharlieBaker2010.com, through his Twitter account.

In his new role as lieutenant gubernatorial candidate, Tisei, who is gay, is speaking publicly about his sexual orientation, which has long been known on Beacon Hill, but not often, if ever, discussed publicly.

Prior to the news conference Monday, in a conversation with the Free Press, Tisei was asked if he feels any relief in speaking publicly about his sexual orientation.

“No, because I wasn’t really hiding,” he said. “I’ve always been pretty open about it, I’ve just never been asked by the press about it before.

“I’ve been elected 13 times and people have always judged me based on my job performance and taking on issues,” he said. “I don’t think people really care about my personal life. It is what it is. It’s not something I think most people ever really cared about.”

Tisei said he and Baker had been discussing potential candidates for lieutenant governor for some time, and he was “pretty surprised” when Baker offered him the position late last week.

“I’m doing this because I really believe that Charlie represents the very best future for the state,” he said. “He’s the right person at the time to get the mess in state government cleaned up and put the state back in the right direction.”

As senate minority leader, Tisei has been one of the most visible critics of Gov. Deval Patrick, even before joining Baker’s team as campaign chairman.

“Most people who watch what happens on Beacon Hill knows it’s been a disaster for the past few years — and it’s not because of the recession,” Tisei said. “Beacon Hill has become dysfunctional and we’re not solving anyone’s problems right now. Even basic things can’t get done. One of the basic things I can help Charlie with is the legislative process. I know how things get done and they don’t get done. I think that’ll be helpful to him to get his agenda accomplished.”

When it comes to legislative process in the state, Tisei has 25 years of experience. He was elected to the House in 1984 at the age of 22 and then ran for and won his current Senate seat in 1991.

Conversely, Baker, who is currently the CEO of Harvard Pilgrim Health Care, has no legislative experience, although he previously served in executive branch positions as the state’s secretary of health and human services and secretary of administration and finance under former Gov. Bill Weld and former Gov. Paul Cellucci.

Tisei has previously drawn parallels between Baker’s campaign and Weld’s campaign in 1990. Baker’s selection of Tisei, who was Weld’s campaign chairman 19 years ago, is another parallel: Weld, who had no legislative experience having served as a federal prosecutor in the U.S. Justice Department, tapped then Sen. Paul Cellucci as his running mate, based in part on Cellucci’s eight-year tenure in the House and six years in the Senate prior to joining Weld’s campaign.

On Monday, Tisei said that the last few Massachusetts governors — “In particular this governor [Deval Patrick]" — have not had productive working relationships with the Legislature. In Patrick’s case, he added, “[this] surprised a lot of people.”

“I’m going to do everything I can help to Charlie win, but [the lieutenant governor candidacy] is more about helping him govern the state when he is elected. It’s not going to be easy.”

Tisei will continue to serve as the senator for his district and as senate minority leader, and is also up for re-election next year.

“It was a tough decision to leave the seat, because I love doing what I’m doing right now,” he said. “People have placed so much confidence in me over the years. I think I can do more for the district and the state as the lieutenant governor. For me, it was the right time.”

Melrose Mayor Rob Dolan, a Democrat, told the Free Press Monday that he wishes the city’s state senator well in his new endeavor.

“Sen. Tisei is an outstanding senator for Melrose, and as mayor I will miss his leadership and influence on Beacon Hill,” Dolan said. “He has forged many positive partnerships with Democrats and independents with his pragmatic approach to issues and consistently excellent constituent services.

“Although we are from different political parties,” the mayor continued, “I have tremendous respect for him and always value his guidance and friendship. I wish him all the best as he seeks this new position during these historically challenging times.”